1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing a heat exchanger tube, more particularly relates to a method and apparatus for cutting into predetermined lengths a tube formed from a thin strip material made of aluminum, copper, etc. for use in a heat exchanger such as a radiator used for dissipating heat from engine coolant water or a heater used for a vehicular air-conditioning system.
2. Description of the Related Art
As a general method used in the past for cutting into predetermined lengths a long hollow tube formed by the method for rolling a thin strip material from its two side edges to continuously form it into a tubular shape or by extrusion or another method, the method of piercing the tube by a cutter and pushing it through to cut the tube is well known. With this cutting method, cutting scraps corresponding to the width of the cutter are produced, so even if these cutting scraps are smoothly discharged, that much material is wasted. If the cutting scraps are not discharged and remain in the tubes, they will interfere with the flow or cause other problems, so it is necessary to provide a scrap reclaiming means etc. in the cutting apparatus to prevent this. This causes the problem of a swelling cost of disposal of the cutting scraps. Further, with tubes formed with partitions in the long direction for dividing the flow path in the tubes into a plurality of parts so as to improve the heat exchange efficiency, there is the problem that cutting scraps particularly easily are left inside the tubes due to the complicated cross-sectional structure.
To solve this problem, the method has been proposed of using a roll cutter to form cutting grooves in advance in a strip material before formation into a tube, then rolling the strip material to form a tubular shape and pulling the formed tube in the longitudinal direction around the cutting grooves to cause tension and generate a large tensile stress at the parts made thinner by the cutting grooves to thereby separate the tube at the groove parts (see Japanese Unexamined Patent Publication (Kokai) No. 63-264218).
This related art used roll cutters to form V-shaped cutting grooves in advance in a strip material before formation into a tube. If the thickness of the material at the parts provided with the cutting grooves became too small, however, stress would concentrate at those parts when rolling the strip material to form it into a tubular shape—resulting in the formation of poorly shaped tubes in some cases. As opposed to this, when the thickness of the material at the parts provided with the cutting grooves became too great, problems would arise such as separation not being possible at the parts of the cutting grooves even if causing tension to act after formation into a tubular shape or the cross-sectional shape of the tube becoming distorted due to the tube being gripped by a strong force at the time of separation, so in the production of tubes using strip materials of particular small thicknesses, there was the problem that it was difficult to maintain the thickness of the parts formed with the cutting grooves in a suitable range not too small or too large—including the problem of wear occurring at the cutting edges of the roll cutters.
Further, as a method of separation of tubes formed with cutting grooves in advance, it is described in the above publication to arrange a plurality of pairs of shaping rolls in a line from small diameters to large diameters and successively pass a strip material provided with the cutting grooves through these pairs of shaping rolls so as to form it into a tubular shape and cause a tensile force to act on the shaped tube in a direction opening the grooves near the cutting grooves. However, to use this method, it is necessary to strongly grip the tube by the pairs of shaping rolls so as to prevent slippage between the shaping rolls and tube surface. If strongly gripping a tube comprised of a thin material between shaping rolls, there is the problem the shaped tube will end up being crushed.
As another related art, the method has been proposed of cutting into predetermined lengths a continuous tube formed into a tubular shape in advance by a prior processing apparatus by using a disk cutter to form cutting grooves in the surface of the tube at the initial step, then gripping a part before a groove by a fixed clamp at the next step and gripping the part after the groove by a movable clamp and rocking it largely in an arcuate shape to bend a predetermined length of the tube and break it off from the following tube part at the cutting groove part (see Japanese Unexamined Patent Publication (Kokai) No. 3-124337).
With this cutting method, however, a disk cutter is used to form cutting grooves at the continuous tube formed into a tubular shape in advance, so in the same way as the above prior art, it is difficult to control the depth of the cutting grooves or the thickness of the material remaining at the parts of the cutting grooves to the optimal ranges. If the thickness of the groove parts becomes too great, the problem may arise of the cross-sectional shape of the tube deforming when bending the tube to break it off. Further, it is necessary to provide a fixed clamp and a movable clamp for rocking with respect to the same for breaking off the tube at the cutting grooves. Therefore, due to the range of rocking of the predetermined length of tube and the size of the space occupied by the device for driving the movable clamp, the cutting apparatus as a whole becomes large in size and complicated in structure. Due to this, a rise in the cost of the cutting step is unavoidably invited.